Radiography refers to a general system, or modality, for recording a radiation image from the transmission of X-rays through the body of a patient. Conventional radiography uses a film/screen combination as the capture device. Such a film/screen can be digitized to produce a digital image. Digital radiography may use either a flat-panel detector (DR) or stimulable phosphor plates (CR). For either digital radiography technology, the output digital signal is usually converted into a unit that is linear with the logarithm of incident exposure. Digital systems can record radiation exposure over a very wide dynamic range, typically on the order of 10,000:1, so that exposure error is seldom a problem.
Due to the wide dynamic range of digital radiography, the raw digital signal produced by the modality will need to be enhanced to produce a visible image suitable for diagnosis by a medical clinician. Image enhancement techniques typically manipulate the spatial frequency components of the image, in order to sharpen edges and to increase the local contrast, and create a tonescale curve, in order to render a visible image with sufficient global contrast.
Algorithms designed to implement an enhancement strategy are usually parameterized by a set of image processing conditions that describe the details of the strategy. Such conditions can specify which spatial frequencies are to be modified, to what degree, and the like. Various image processing algorithms are known to those skilled in the art. For example, refer to U.S. Pat. No. 5,978,518 (Oliyide) and U.S. Pat. No. 6,069,979 (VanMetter).
Image processing, however, is not fully responsible for the quality of the presented image. The precursor to a well-rendered image is a proper acquisition. Example requirements for a properly acquired image are: proper alignment and distance of the X-ray source to the acquisition device, proper technique factors for the body part being imaged (kVp, mAs), minimal scatter which can be mitigated by proper use of collimation and scatter-reduction grids, high resolution acquisition devices when warranted, etc. The present invention addresses the need to have a variety of available acquisition choices including anti-scatter grids and image resolution based on exam type.
The use of grids has been recommended for X-ray radiography when Gustave Bucky introduced the first stationary grid for scatter reduction yielding image contrast improvement. Refer to U.S. Pat. No. 1,164,987 (Bucky) which issued in 1915. Accordingly, these devices are commonly found in most radiology departments and available in many configurations.
A grid typically includes of a series of lead foil strips separated by X-ray-transmissive spacers. The spacing of the strips determines the grid frequency, and the height-to-distance ratio determines to grid ratio. Grids can be oriented horizontally or vertically. Two general methods of use exist for grids: stationary and moving. With stationary grids, grid lines will leave shadows in the radiographic image. With a moving grid, the grid lines are intentionally blurred out by the motion.
In the case of stationary grid lines, the high frequency grid pattern, in combination with the scanning frequency of the scanning system, may cause an image artifact viewable on a soft copy display. This is caused by aliasing, which is introduced by the discrete sampling of the high frequency lead strips in the image by the scanning system. Grid suppression algorithms are known. For example, refer to U.S. Pat. No. 6,269,176 (Barski), commonly assigned. Such a suppression algorithm may be used to isolate and suppress this artifact. Also, if a moving grid system is rendered inoperable, stationary lines will be imaged in the latent image and a grid detection method such as in U.S. Pat. No. 5,661,818 (Gaborski) issued Aug. 26, 1997 and the above mentioned grid suppression algorithm could be of interest.
Optional grid detection and suppression is situation dependent. In the situation of a cassette with an imbedded grid, as in U.S. Pat. No. 5,008,920 (Gralak) issued Apr. 16, 1991, detection may not be desired if the grid resolution is specified.
Image resolution is another optionable acquisition characteristic, and, for computed radiography (CR) which employs storage phosphor, is dependent upon the cassette phosphor and the capabilities of the CR scanning device. A cassette having a high-resolution phosphor may be read on a CR scanner with more than one scanning speed or laser characteristic (i.e. power, spot size, and the like). Applicants have recognized that a method or user interface to choose these available options can be used to indicate the anticipated scan sequence.
A component to image quality as influenced by acquisition is CR scanner calibration. Calibration is necessary for adjusting the differences in machine hardware and setup. By adjusting for variances, a calibration profile will give the same quality images on each machine when calibrated correctly. The goal of the calibration is to expose a plate to a uniform exposure and adjust each gain so the value read from the plate are not only uniform but of a value equal or close to the actual exposure of the plate. Choosing this correctly can have an impact on the contrast to noise characteristics of a low exposure image.
The use of identification codes on cassettes is known, such as described in U.S. Pat. No. 4,960,994 (Muller) issued on Oct. 2, 1990, U.S. Pat. No. 5,264,684 (Weil) issued Nov. 23, 1993, U.S. Pat. No. 5,334,851 (Good) issued Aug. 2, 1994, U.S. Pat. No. 5,418,355 (Weil) issued May 23, 1995, U.S. Pat. No. 5,592,374 (Fellegara) issued Jan. 7, 1997, U.S. Pat. No. 5,646,416 (VandeVelde) issued Jul. 8, 1997, U.S. Pat. No. 5,757,021 (Dewaele) issued May 26, 1998, and U.S. Pat. No. 6,379,044 (Vastenacken) issued Apr. 30, 2002. Identification codes are used to: identify patients; identify phosphor screen; identify image particulars such as body part, X-ray exposure conditions, and technique deviations from expected exposures; link patients with their image data; and control aspects of acquisition.
U.S. Pat. No. 5,027,274 (Takayanagi) issued Jun. 25, 1991, describes a management system to link and handle CR image data, a patient identification photograph and technique information. However, there is no control of the CR scanner.
The use of radio frequency tags for CR applications is known, for example, see U.S. Pat. No. 6,271,536 (Buytaert) issued Aug. 7, 2001 and U.S. Pat. No. 6,359,628 (Buytaert) issued Mar. 19, 2002, which are directed to a radiographic image identification method including an radio frequency tag.
Accordingly, there exists a need for an apparatus and method where post-acquisition options, such as scanning speeds, system calibration, various grid options and processing algorithms, are available.
The present invention addresses the need for flexibility in the current CR market, where post-acquisition options, such as scanning speeds, system calibration, various grid options and processing algorithms, are available.